Bolster spring



FIG. 1 is a perspective top and left side view of a bolster spring having the inventive design;

FIG. 2 is a rear view of the bolster spring shown in FIG. 1;

FIG. 3 is a front view of the bolster spring shown in FIG. 1;

FIG. 4 is a left side view of the bolster spring shown in FIG. 1;

FIG. 5 is a right side view of the bolster spring shown in FIG. 1;

FIG. 6 is a top view of the bolster spring shown in FIG. 1; and,

FIG. 7 is a bottom view of the bolster spring shown in FIG. 1.

The broken lines in the drawings are for the purpose of illustrating portions of the bolster spring that form no part of the claimed design. Portions of the bolster spring shown in broken lines form no part of the claimed design. 

CLAIM The ornamental design for a bolster spring, as shown and described. 